When drying pharmaceutical compounds by evaporation, such as centrifugal evaporators, it can be important that the material being evaporated is not subjected to temperatures that could damage one or more of the sample components making up the mixture. However, in order to achieve rapid evaporation heat has to be supplied to the sample material during evaporation to balance the heat lost due to the evaporation (the latent heat) of the solvent. In order to achieve these two, possibly conflicting, requirements, it is necessary to accurately monitor the temperature of the sample material, for example to ensure that certain maximum temperatures are not exceeded.
UK Patent Specification 2334688 describes the use of temperature sensing probes placed in or adjacent to samples in a chamber with means for transferring the temperature data from a sensor on the rotor to a system controller remote from the rotor typically external of the chamber. UK Patent Application 0105345.3 describes the use of a non-contact temperature sensing device to sense the temperature of a disc rotor, in which sample containers are fixed in position.
Problems arise when employing a non-contact sensing device in a chamber in which the sample containers move (typically swing upwardly and outwardly) as a rotor gathers speed to generate centrifugal forces on the sample material in the containers.
In general, non-contact temperature sensing devices have a wide field of view. Even so, a single temperature sensing device will only ‘see’ the swing during part of each rotation of the rotor. Heat transfer between rotor and swing is usually poor, so that if for example heat is supplied by an infra-red (IR) lamp, when the IR lamp is on, the rotor win tend to become heated to a significantly higher temperature than the or each swing, and the sample material in containers such as test tubes therein. Therefore if the sensor is also responsive to the rotor temperature (as is usually the case), this will cause the temperature information from the sensor to suggest a higher sample temperature than will actually exist in the sample material.
Non-contact temperature sensing devices often employ a viewing window (lens), which tends to be susceptible to contamination during evaporation, thus interfering with the temperature monitoring function.
It is an object of the present invention to provide an improved system for non-contact temperature measurement and for viewing the evaporation process in a centrifugal evaporator.